1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member for use in the electrophotographic process, in which the outermost layer is a non-monocrystalline carbon film containing hydrogen (hereinafter referred to as "a-C:H").
2. Related Background Art
In the technology of device members used for the electrophotographic photosensitive member, there have been proposed various materials including selenium, cadmium sulfide, zinc oxide, phthalocyanine, amorphous silicon (hereinafter referred to as "a-Si"), and so on. Among others, proposed as high-performance, highly durable, and nonpolluting photosensitive members are non-monocrystalline deposited films comprising silicon atoms as a principal component, typified by a-Si, for example, amorphous deposited films such as of a-Si compensated with hydrogen and/or halogen (for example, fluorine, chlorine, etc.) or the like, some of which are put in practical use. As the forming method of such deposited films, there have been hitherto known a number of methods such as a sputtering method, a method of decomposing a source gas with heat (thermal CVD method), a method of decomposing a source gas with light (photo CVD method), a method of decomposing a source gas with plasma (plasma CVD method), and so on. Among them, the plasma CVD method is a method of decomposing a source gas by glow discharge induced by direct current, high frequency (RF, VHF), microwave, or the like and thereby forming a thin deposited film on a substrate of such a material as glass, quartz, heat-resistant synthetic resin film, stainless steel, aluminum and so on, and has been put to practical use considerably in the method of forming an a-Si deposited film for electrophotography or the like. A variety of apparatuses for practicing the method have also been proposed.
For example, Japanese Patent Application Laid-Open No. 57-115551 discloses an example of a photoconductive member in which a surface barrier layer comprised of a non-photoconductive amorphous material comprising silicon and carbon atoms as a matrix and hydrogen atoms is provided on a photoconductive layer comprised of an amorphous material comprising silicon atoms as a matrix and at least either of hydrogen atoms or halogen atoms.
Further, Japanese Patent Application Laid-Open No. 61-219961 discloses an example of an electrophotographic photosensitive member in which a surface protecting layer formed on an a-Si based photosensitive layer is comprised of a-C:H containing 10-40 atomic % of hydrogen atoms.
Japanese Patent Application Laid-Open No. 6-317920 discloses a method of producing an electrophotographic photosensitive member formed of a photoconductive layer comprised of a non-monocrystalline silicon based material comprising silicon atoms as a matrix, and an a-C:H surface protecting layer containing 8-45 atomic % of hydrogen atoms, using a high-frequency wave of the frequency not less than 20 MHz.
Further, Japanese Patent Application Laid-Open No. 60-186849 discloses a method and apparatus for forming an electrophotographic device having a top inhibiting layer formed by the microwave plasma CVD method using the microwave (for example, of the frequency 2.45 GHz) as a source gas decomposing means.
These techniques improved the electrical, optical, and photoconductive characteristics, operating circumstance characteristics, and durability and further implemented improvement in image quality.
However, the electrophotographic devices tend to increase the operation speed and lifetime further in recent years. Under such circumstances, even the electrophotographic photosensitive members, which have demonstrated sufficient performance heretofore, might suffer, for example, fusion in certain cases, depending upon the operating circumstances or the structure of the main body of electrophotographic apparatus. The "fusion" is a phenomenon in which a toner melts to adhere to a surface of the electrophotographic photosensitive member during long-term use. The adhesion, depending upon the degree thereof, will result in fusion marks in a solid white image or in a halftone image and will pose a problem in practical use. With occurrence of such fusion resulting in the fusion marks on the image, a service technician has to visit a customer to perform maintenance, which requires an extra maintenance fee. Since the maintenance was carried out after the photosensitive member was dismounted from the main body of electrophotographic apparatus, there was a risk of scratching the photosensitive member during the work to disable it.
In recent years, while development of OA devices which are harmless to the global environment is driven under leading by nations and governments, the tendency of saving of energy and resources is becoming stronger and stronger than before in the field of the electrophotographic apparatus as well. Efforts have been made from various aspects on the energy and resources saving in the electrophotographic apparatus and an example among them is an attempt of power saving of a fixing unit for fixing a toner onto paper. In the conventional apparatuses, the fixing unit is provided internally with a heater to always maintain a fixing roller at 150.degree. C. to 200.degree. C. and to melt the toner, thereby fixing it onto paper. Power consumption of the fixing unit can be decreased by lowering the maintained temperature of the fixing roller. In this case, in order to avoid fixing failure of a toner, the toner used is also switched to a low-melting-point toner capable of being melted to be fixed at a lower temperature. In this case, there arise no practical problems as to the image quality and the fixing property. However, when such a low-melting-point toner was used, there were some cases where the fusion stated previously became easy to occur, depending upon combination of the operating circumstances of the electrophotographic apparatus, components in the toner, the surface property of the electrophotographic photosensitive member, urging pressure of a cleaner, processing speed, and so on.
Further, since the color toner used in a full color electrophotographic apparatus was originally a low-melting-point toner, the circumstances thereof were originally such that the fusion was easy to occur.
A conceivable method of preventing this fusion is a method of polishing the surface of the electrophotographic photosensitive member to shave off the fusion source together with the film surface. However, in the case of the electrophotographic photosensitive member with high hardness of the a-Si type, the surface was not shaven into a smooth surface, but uneven shaving occurred in a stripe pattern. This uneven shaving of the stripe pattern appeared on the image and it was common practice heretofore to use the a-Si type electrophotographic photosensitive member under such conditions as not to cause shaving of surface.
Another method of preventing the fusion is a method of adding silica or the like as an abrasive to the toner itself, changing the component thereof, or increasing the quantity thereof. When the toner itself contains the abrasive, the capability of rubbing the drum surface is enhanced thereby, so that the melted toner becomes less likely to adhere to the surface. However, this can prevent the fusion on one hand, but the capability of rubbing the surface of photosensitive member is also enhanced as a side effect on the other hand. Therefore, it was difficult to strike a balance within the range in which only the fusion was improved without shaving the surface of the photosensitive member.
Further, in order to prevent the fusion, there has been employed a method of increasing the urging pressure of the cleaner and scraping off all the toner to keep the toner from adhering to the surface. However, in order to prevent polishing of the surface of photosensitive member while preventing the fusion, a delicate balance is also required. Therefore, there has been the problem that it is difficult to constantly prevent the fusion for all of electrophotographic apparatuses under mass production.